Cellulose solutions and products made therefrom

ABSTRACT

An optically anisotropic solution containing cellulose and inorganic acids of phosphorus contains 94-100 wt % of the following constituents: cellulose; phosphoric acid and/or its anhydrides; and water; and 0-6 wt % of other constituents. This solution can be prepared in an apparatus in which intensive mixing is made possible by the shearing forces generated by mixers and kneaders in the apparatus. The solution can be used in making pulp, hollow fibres, staple fibre, membranes, nonwovens, or films.

This is a divisional application of U.S. application Ser. No.08/793,815, filed on Feb. 25, 1997, which is now U.S. Pat. No.5,817,801.

The invention pertains to an optically anisotropic solution containingcellulose and inorganic acids of phosphorus, a process for preparingsuch solutions, the making of products therefrom, and the products thusobtained.

Japanese patent publication JP 4258648 discloses cellulose solutions inwhich at least cellulose, water, and a mixture of two acids areemployed. The description states that, in order to effect properdissolution of the cellulose, the solvent may not contain in excess or85 wt. % of ortho-, meta-, pyro-, or polyphosphoric acid. Cellulosesolutions exhibiting optical anisotropy are obtained by mixing sulphuricacid, ortho- or polyphosphoric acid, and water in a weight ratio of10-20/70-80/10-20 and dissolving at least 15 wt. % of cellulose therein.

Such optically anisotropic solutions containing cellulose and aninorganic acid of phosphorus are also described in an article by K.Kamide et al. of Asahi Chemical Industry Co., "Formation and Propertiesof the Lyotropic Mesophase of the Cellulose/Mixed Inorganic AcidSystem," Polymer Journal Vol. 25, No. 5 (1993), 453-461. This articleclearly indicates that anisotropic solutions can only be obtained with amixture of sulphuric acid/polyphosphoric acid/water as solvent and atleast 16 wt. % of cellulose.

Sulphuric acid has a highly oxidative effect on cellulose, causing it todegradate. In addition, the use of sulphuric acid promotes corrosion andso is less advisable for industrial applications. A further drawbackconsists in that the use of a mixture of different acids such assulphuric acid and phosphoric acid is disadvantageous in industrialapplications, while recovering the solvent after manufacture of theproduct from a solvent system containing several acids was likewisefound to be disadvantageous. The system as mentioned in the aforesaidarticle does not permit a great deal of control over major processsettings, since with only one anisotropic system being deemed feasible,the viscosity and the proper temperature are all but fixed.

The present invention relates to an anisotropic solution of cellulosewhich obviates the aforementioned drawbacks. The invention relates to ananisotropic solution according to the preamble of the claim, and ischaracterised in that the solution contains 94-100 wt. % of thefollowing constituents:

cellulose,

phosphoric acid and/or its anhydrides, and

water.

In the present patent specification the solvent is made up, bydefinition, of the added phosphoric acid and/or anhydrides thereof, andall the water present in the solution which is not chemically bonded.For that reason, water derived from the cellulose that is generallyadded at a later time is always considered to be part of the solvent inthis description, as is water from substances which are among "otherconstituents", which substances may be added at any time during thepreparation of the solution.

The term phosphoric acid in this application stands for all inorganicacids of phosphorus, including mixtures thereof. Orthophosphoric acid isan acid of pentavalent phosphorus, i.e., H₃ PO₄. The anhydrousequivalent thereof, i.e., the anhydride, is also known as phosphoruspentoxide (P₂ O₅). Depending on the amount of water in the system, thereis, in addition to orthophosphoric acid and phosphorus pentoxide, aseries of pentavalent phosphoric acids with a water-binding capacitybetween the pentoxide and the ortho-acid. Alternatively, solvents of,say, orthophosphoric acid with a concentration of orthophosphoric acidof less than 100% may be used.

Due to some reaction between the phosphoric acid and the cellulose, thesolution may contain phosphorus derivatives of cellulose. Thesederivatives of cellulose are also considered to belong to theconstituents making up 94-100 wt. % of the solution. Where thepercentages by weight of cellulose in solution listed in this patentspecification concern phosphorus derivatives of cellulose, they relateto quantities calculated back on the cellulose. The same holds for theamounts of phosphorus mentioned in this specification.

The anisotropic solution

Already at a cellulose concentration of 8% in a solution of phosphoricacid according to the invention anisotropy was observed, and anisotropicsolutions were still obtained at cellulose concentrations of 40% orhigher. Such high concentrations preferably are prepared at elevatedtemperatures. Selecting a cellulose concentration of more than 8% givesa significantly more economical method of making products from thesolutions. Thus anisotropic cellulose solutions can be obtained byselecting a cellulose concentration in the range of about 8 to 40%.Optimum processing of these solutions into fibres was found to beattained in the range of 10 to 30%, preferably 12.5 to 25%, moreparticularly 15 to 23%. Different fields of application of the solutionsmay have other optimum concentration ranges.

To obtain the solvent system by means of which anisotropic solutionsaccording to the present invention can be attained, the phosphoruscontent is determined by converting the quantities by weight ofphosphoric acid in the solvent into the equivalent quantities by weightof the corresponding anhydride. Converted in this way, orthophosphoricacid is composed of 72.4% of phosphorus pentoxide and residual water,while polyphosphoric acid H₆ P₄ O₁₃ is composed of 84% of phosphoruspentoxide and residual water.

The concentration of P₂ O₅ in the solvent is calculated by starting fromthe overall quantity by weight of inorganic acids of phosphorus andtheir anhydrides, and the overall amount of water in the solvent,converting the acids into water and P₂ O₅, and calculating whichpercentage of said overall quantity by weight is made up of P₂ O₅. Ifother phosphoric acids are employed, the conversion into thecorresponding anhydrides is carried out analogously.

According to the teaching of Japanese patent publication JP 4258648, itis possible to obtain anisotropic solutions by randomly replacing onephosphoric acid with another, taking into account that the weightpercentage of the replacer acid in the solution is the same as that ofthe replaced acid.

By contrast, it has now been found that anisotropic solutions accordingto the present invention cannot be obtained by randomly replacing onephosphoric acid with another while taking into account that the acidweight percentages in the solution stay the same, but that it is aquestion of randomly replacing one acid with another as long as thepercentage calculated back on the anhydrides is kept within certainlimits. A particular part in forming anisotropic solutions according tothe invention is played by the water content of the solvent, includingthe amount of water in the cellulose and in the acid.

If a phosphorus system contains acids of pentavalent phosphorus, thesolvent for preparing the solution according to the invention willcontain 65-80 wt. % of phosphorus pentoxide, preferably from 70 to 80wt. %. In a most preferred embodiment of the present invention, asolvent containing from 71 to 75 wt. % of phosphorus pentoxide is usedfor preparing anisotropic solutions containing 8 to 15 wt. % ofcellulose, and a solvent containing from 72 to 79 wt. % of phosphoruspentoxide is used for preparing anisotropic solutions containing 15 to40 wt. % of cellulose.

In addition to water, phosphoric acid and/or anhydrides thereof,cellulose, and/or reaction products of phosphoric acid and celluloseother substances may be present in the solution.

For instance, solutions can be prepared by mixing constituentsclassifiable into four groups: cellulose, water, inorganic acids ofphosphorus and their anhydrides, and other constituents. The "otherconstituents" may be substances which benefit the processability of thecellulose solution, solvents other than phosphoric acid, or additives,e.g., to counter cellulose degradation as fully as possible, or dyes andthe like.

The solution according to the present invention is composed of 94-100wt. % of cellulose, phosphoric acid and/or anhydrides thereof, andwater. Preferably, the solution is composed of 96-100 wt. % ofcellulose, phosphoric acid and/or anhydrides thereof, and water.Preferably, adjuvants or additives are present only in an amount of 0 to4 wt. %, calculated on the overall quantity by weight of the solution.More favoured still is a solution containing the lowest possible amountof substances other than the constituents cellulose, phosphoric acidand/or anhydrides thereof, and water, i.e., from 0 to 1 wt. % ofadditives.

Preparation of the anisotropic solution

Russian patent publications SU 1348396 and SU 1397456 provide severalexamples of the preparation of solutions of cellulose in phosphoricacid. The overall period of time required to obtain a homogeneoussolution ranges from 2 to 400 hours. Moreover, it was found that thereis a sharp and uncontrolled decrease of the degree of polymerisationduring the preparation of the solution.

It is undesirable, when making solutions according to the presentinvention on an industrial scale, to need long periods to dissolve inview of the then required size of the storage/dissolving tanks.Furthermore, the continuous preparation of such solutions is hindered bylong periods needed to dissolve. Also, a sharp, uncontrolled decrease ofthe cellulose DP can be disadvantageous as regards the further use ofthe solution, e.g., when the solution is employed to make cellulosefibres. An uncontrolled decrease of the DP during the preparativeprocess will also make it more difficult to prepare a solution of fairlyconstant quality, more particularly when various types of cellulose areused in the preparation of the solution.

It is clear from the aforementioned patent publications that dissolvingcellulose in a solvent primarily containing phosphoric acid will take along time.

U.S. Pat. No. 5,368,385 discloses that the dissolution in water ofpolymers which are extremely soluble in water is severely hampered bythe formation of a impermeable film on the wetted surface of formedpolymer lumps. Without wishing to be bound by any theory, applicantsupposes that during the dissolution of cellulose particles inphosphoric acid the outer layer of the cellulose employed dissolvescomparatively quickly to form an impermeable layer, analogous to thedisclosure of U.S. Pat. No. 5,368,385. It is this impermeable layerwhich hampers/slows down the further dissolution of the celluloseenclosed by it. Several processes were found which provide an answer tothis problem.

One answer can be seen to lie in the very rapid and thorough mixing ofcellulose and the phosphoric acid-containing solvent, the mixing actionpreferably being such as will give particulate cellulose in the solventbefore the formation of a too thick impermeable layer around the piecesof cellulose can slow down further dissolution too much. The rate atwhich the impermeable layer is formed, i.e., the rate at which thecellulose is dissolved in the phosphoric acid-containing solvent, can bedecreased by lowering the temperature at which the cellulose iscontacted with the solvent. When there is particulate cellulose in thesolvent, said particulate cellulose preferably is on a micro scale,e.g., in the form of cellulose fibrils, dissolution of these smallpieces in a short time will give a solution containing cellulose andinorganic acids of phosphorus.

Alternatively, an answer can be seen to lie in so processing thecellulose during its mixing with the phosphoric acid-containing solventthat the impermeable outer layer formed on the cellulose is removedtherefrom with great regularity.

The mixing of cellulose and the phosphoric acid-containing solvent willproceed more rapidly as the cellulose in the solvent is in smallerpieces. To this end the cellulose may already be rendered particulate,e.g., by being pulverised, prior to being combined with the solvent.Alternatively, the cellulose and the solvent can be combined in such anapparatus as will not only provide intermixing of the cellulose and thesolvent but also a reduction in size of the pieces of cellulose presentin the mixture.

When preparing a cellulose-containing solution using cellulose and aphosphoric acid-containing solvent, three steps can be distinguished inaddition to combining the cellulose and the solvent, viz.:

1 reducing the cellulose in size,

2 mixing the cellulose and the phosphoric acid-containing solvent, and

3 dissolving the cellulose in the solvent.

Given the rate at which cellulose is dissolved in a phosphoricacid-containing solvent, steps 2 and 3 cannot be consideredindependently. When the cellulose and the solvent are intermixed, thecellulose will also dissolve in the solvent. As has been indicatedabove, the dissolution of the cellulose can be slowed down by loweringthe temperature.

Step 1 can be dissociated from steps 2 and 3. One example of this is thepreparation of a solution from powdered cellulose and a phosphoricacid-containing solvent.

As has been indicated above, it is also possible to combine all threesteps, i.e., by combining the reduction in size, mixing, and dissolutionof the cellulose in a single apparatus equipped such that the cellulosecan be reduced in size and mixed in the presence of the solvent.

Especially when cellulose solutions are to be prepared on aneconomically attractive scale, it is advantageous to combine theaforesaid three steps in a single apparatus, especially if it provespossible to prepare a cellulose solution in such an apparatus in acontinuous process, i.e., a preparative process in which startingmaterials are fed to the apparatus in a more or less constant streamwhile a cellulose solution is discharged from the apparatus also in amore or less constant stream.

It was found that solutions according to the present invention can beprepared if cellulose and the phosphoric acid-containing solvent arecombined in an apparatus in which the shearing forces generated by itsmixers and kneaders ensure that there can be intensive mixing of one ormore added constituents. In a suitable embodiment the mixing andkneading apparatus used to practice the process according to theinvention is a high-shear mixer. Examples of high-shear mixers known tothe skilled person include a Linden-Z kneader, an IKA-duplex kneader, aConterna kneader, or a twin-screw extruder.

A highly suitable embodiment involves making use of an apparatus whichalso permits particle size reduction. Preferably, the high-shear mixeralso permitting particle size reduction is a twin-screw extruder.

By proper selection of the mixing, kneader, and milling units and theirorder on the shafts of a twin-screw extruder many different forms ofcellulose, such as sheets, strips, scraps, chips, and powder, can bereduced in size where needed and mixed thoroughly with the phosphoricacid-containing solvent before the dissolution of the cellulose in thesolvent is slowed down too much by the formation of an impermeablelayer.

After combination of the phosphoric acid-containing solvent and thecellulose in a mixing or kneading apparatus, the cellulose is mixed withthe solvent and there is cellulose dissolution. The degree of mixingshould be such as will prevent the cellulose dissolution being sloweddown too much by the formation of an impermeable layer on the cellulose.The cellulose dissolution can be slowed down by lowering thetemperature. One advantageous process involves the cellulose and thesolvent being combined in an apparatus, with the temperature in thesection of the apparatus where the cellulose and the solvent arecombined and mixed being less than 30° C., preferably in the range of 0°C. to 20° C. In another favourable embodiment the solvent, prior tobeing combined with the cellulose, is cooled such that its temperatureis below 25° C. In that case the solvent can be either in the solid orin the liquid state. It is possible to cool the solvent, prior to beingcombined with the cellulose, in such a way as to be in the form of smallpieces of solid solvent.

According to another advantageous embodiment, first a portion of thesolvent is mixed with the-cellulose, after which the remaining solventis added to the formed mixture/solution in one or several steps.

An advantageous process will have the apparatus constructed such thatduring the mixing and kneading the starting products and the formedsolution are conveyed from an opening in the apparatus where the solventand the cellulose are combined to another opening where the solutionleaves the apparatus. Examples of such apparatus include a Conternakneader, a twin-screw extruder, an Linden-Z kneader, and a Buschco-kneader.

In a favourable embodiment of the process a twin-screw extruder is usedas mixing and kneading apparatus with a conveying system.

In such an apparatus there may be several different zones for theproducts in the apparatus to pass through. In the first zone there willbe primarily mixing of the supplied cellulose with the solvent andreduction in size. In the next zone the dissolution of cellulose willalso play a major part. The subsequent zone will primarily hold theformed solution, which is subjected to further homogenisation and mixedwith the as yet undissolved cellulose.

In such an apparatus the dissolution of cellulose and the properties ofthe formed solution can be affected by the temperature selected for thevarious zones.

By selecting a temperature for the first zone which is below 30° C.,preferably in the range of 0° to 20° C., the dissolution of cellulosecan be slowed down. By increasing the temperature, e.g., in a next zone,cellulose dissolution is speeded up. It should be noted in thisconnection that heat may be generated both during cellulose dissolutionand as the solvent and the cellulose are combined.

By selecting the temperature and the residence period in the zone of themixing and kneading apparatus which primarily contains cellulose insolution, the cellulose solution DP can be controlled. Generallyspeaking, it holds that the higher the temperature and the longer theresidence period at this temperature are, the greater the decrease ofthe cellulose DP will be. In addition, the DP of the starting materialmay have an effect on the decreasing DP for a particular temperature andresidence period.

Since the heat exchange between the products in the apparatus and theapparatus itself will not be ideal as a rule, there may be temperaturevariations between the products in the apparatus and the apparatusitself.

The apparatus can further have a zone in which the formed solution isde-aerated, e.g., by passing the solution through a reduced pressurezone. Also in this zone or in a separate zone water or otherconstituents may be extracted from or added to the formed solution.

To remove any remaining small undissolved particles from the solution,it may be filtered either in the apparatus or on leaving it. Theresulting solution is high-viscous. It can be used immediately, but alsostored for some time at low temperature, e.g., between -20° and 10° C.Generally speaking, the longer it is desired to store the solution, thelower the temperature selected should be.

It should be noted that the obtained solution may become solid, e.g.,through crystallisation, if it is stored for some time at a lowertemperature. Heating the formed solid mass will again give ahigh-viscous solution.

The above process makes it possible to prepare cellulose solutions in ashort period of time and with a controlled decrease of the cellulose DP.For instance, it was found that within 15 minutes or even less acellulose solution could be made from powdered cellulose and a solventcontaining phosphoric acid. This time period can be further reduced byselecting a higher temperature for forming the solution.

The solution according to the invention can be prepared using allavailable types of cellulose, such as Arbocell BER 600/30, Arbocell L600/30, Buckeye V5, Buckeye V60, Buckeye V65, Viscokraft, hemp, flax,ramie and Eucaliptus cellulose, all of which types are known to theskilled person. Cellulose can be added in a wide range of forms, e.g.,in sheets, strips, scraps, chips, or as a powder. The form in which thecellulose can be added is restricted by its introduction into the mixingand kneading apparatus. If the cellulose employed is in a form whichcannot be charged to the apparatus, it should be reduced in size outsidethe apparatus in a known manner, e.g., with a hammer mill or a shredder.

The cellulose to be used preferably has an α-content of more than 90%,more particularly of more than 95%. For spinning good fibres from thesolutions it is recommended to employ so-called dissolving pulp with ahigh α-content, e.g., such as is generally used in the manufacture offibres for industrial and textile applications. Examples of suitabletypes of cellulose include Arcobell BER 600/30, Buckeye V60, BuckeyeV65, and Viscokraft. The cellulose DP as determined by the procedure tobe indicated hereinafter in this patent specification advantageously isin the range of 250 to 1500, more particularly in the range of 350 to1350. The DP of the cellulose in the solution preferably is in the rangeof 215 to 1300, more particularly in the range of 325 to 1200.

Cellulose as it is commercially available generally contains some waterand may be used as such without any objection. Of course, it is alsopossible to use dried cellulose, but this is not essential.

If use is made of a mixture of different inorganic phosphoric acids toobtain a solvent having the desired quantity of acid converted intoanhydride, the acids after being mixed preferably are heated to atemperature in the range of 30° to 80° C. and the solvent is kept heatedfor 1/2-12 hours. In some cases, depending on the acids used, othertimes and/or temperatures may be desired. For instance, a veryhomogeneous solution without surface irregularities can be obtained byemploying a solvent made by melting down orthophosphoric acid at atemperature in the range of about 40° to 60° C., adding the desiredquantity of polyphosphoric acid, mixing the two, and cooling the mixtureto about 20° C.

According to a suitable method, the solvent is left to stand some time,e.g., between 30 minutes and several hours, before being combined withcellulose.

The other constituents can be added to the solvent prior to itscombination with the cellulose. Alternatively, the other constituentscan be added to the cellulose prior to its combination with the solvent.Also, the other constituents can be added as the solvent is combinedwith the cellulose. In addition, of course, the other constituents canbe added after the solvent and the cellulose have been combined.

Time, the temperature at which the solution is stored, and the acidconcentration were all found to have a major effect on the content ofphosphorus bound to cellulose in the solution.

Phosphorus is assumed to be bound to cellulose if, after a thoroughwashing treatment and, optionally, a neutralisation treatment, acoagulated solution is still found to contain phosphorus.

It was found that a solution according to the present inventioncontaining 18 wt. % of cellulose, which was obtained by dissolvingcellulose in a solvent containing 80 wt. % of orthophosphoric acid and20 wt. % of polyphosphoric acid, will contain approximately 0.25 wt. %of bound phosphorus after storage for 1 hour at 30° C. However, if sucha solution is stored at 50° C., it will contain approximately 0.8 wt. %of bound phosphorus after 1 hour.

It was found that a solution according to the invention will at any ratecontain at least 0.02% of phosphorus bound to cellulose.

It was found that by adding a small quantity of water to the solventjust prior to the addition of the cellulose, simultaneously with theaddition of cellulose, or just after the addition of cellulose, asolution with a low content of phosphorus bound to cellulose can beobtained.

The obtained solution can be used to various ends. For instance, thesolution can be used in making fibres, both for industrial and textileapplications, hollow fibres, membranes, nonwovens, films, and for otherwell-known applications for cellulose-containing solutions. In addition,the solution can be employed to prepare cellulose derivatives.

Spinning the anisotropic solution

The obtained solution can be spun or extruded through a spinneret havingthe desired number of orifices, or moulded to form a film. Spinningsolutions with a cellulose concentration of from 15 to 25 wt. %preferably are extruded at a temperature between 0° and 75° C., theresidence times for the higher temperatures being as brief as possible.Preferably, such solutions are extruded at a temperature between 20° and70° C., more particularly between 40° and 65° C. For otherconcentrations it holds that as the concentration is higher, so thespinning temperature preferably will also be higher than the rangesindicated here to compensate, int. al., for the higher viscosity of thesolution, and vice versa. However, it should be noted that a higherspinning temperature may lead to a higher content of phosphorus bound tocellulose.

The desired number of orifices in the spinneret plate is dependent onthe future use of the fibres to be obtained. Thus, a single spinneretmay be used not only for extruding monofilaments but also for extrudingthe multifilament yarns much in demand in actual practice which containfrom 30 to 10 000, preferably from 100 to 2000, filaments. Themanufacture of such multifilament yarns preferably is carried out on acluster spinning assembly containing a number of spinning orificeclusters as described in EP 168 876, or using a spinneret as describedin WO 95/20696.

Following extrusion, the extrudates are passed through an air gap thelength of which is selected depending upon the process conditions, e.g.,the spinning temperature, the cellulose concentration, and the desireddegree of drawing of the extrudates. In general, the air gap will have alength in the range of 4 to 200 mm, preferably in the range of 10 to 100mm. Next, the obtained extrudates are passed through a coagulation bathin a manner known in itself. As suitable coagulants may be selected lowboiling, organic liquids which do not have a swelling effect oncellulose, water, or mixtures thereof. Examples of such suitablecoagulants include alcohols, ketones, esters, and water, or mixturesthereof. Preference is given to the use of isopropanol, n-propanol,acetone or butanone as coagulants, since they display very goodcoagulating action and in most cases have good properties when it comesto safety and ease of handling. For this reason mixtures of water andthese coagulants also are very serviceable.

The coagulation bath preferably has a temperature in the range of -40°C. (providing the coagulant selected allows this) to 30° C., with veryfavourable results being obtained at coagulation bath temperatures below20° C.

After coagulation there may be washing out, in combination or not with aneutralising treatment. The washing out may take the form of placing aspool of coagulated yarn in a vessel containing the washing agent, orelse by passing the fibres through a bath containing the appropriateliquid in a continuous process and then winding them onto a roller.According to a process highly suited for use in actual practice, washingout is performed with so-called jet washers, such as described inBritish patent specification GB 762,959. Low boiling, organic liquidswhich do not have a swelling effect on cellulose, e.g., alcohols,ketones, and esters, water, or mixtures thereof can be employed aswashing agent. Preference is given to the use of isopropanol,n-propanol, butanone, water, or mixtures thereof as washing agent.Highly suitable to be used are water, or mixtures of water and thecoagulation agent. Washing out may be performed at any temperature belowthe boiling temperature of the washing agent, at any rate preferablybelow 100° C.

It was found that when a solution according to the invention is storedfor a longer period of time or at elevated temperature, it cannot bespun into fibres by an air gap spinning process if the solution iscoagulated in a water bath or if, after coagulation, the fibres arewashed with water, since the fibres will swell to a great extent whencontacted with water.

It was also found that if the quantity of water absorbed by a fibreduring coagulation in a water bath or when the fibre is washed out in awater bath is higher than 560% in relation to the dry weight of thefibre, then the individual fibres in the bundle can no longer bedistinguished. A water absorption higher than 1300% will give gelformation. To make fibres having favourable mechanical properties, it ispreferred to have a fibre moisture absorption of less than 570%.

It was found that a lower content of phosphorus bound to cellulose willalso give a lower moisture absorption. It was found that if the solutionaccording to the invention contains less than 3 wt. % of boundphosphorus and the solution is coagulated in a bath which contains lessthan 10 wt. % of water, e.g., an acetone coagulation bath, and the fibreis washed out in a water bath, the individual fibres in the bundle aclearly distinguishable still. It was further found that if the solutioncontains less than 1.3 wt. % of bound phosphorus and the solution iscoagulated in water, the individual fibres in the bundle are clearlydistinguishable still during water washing.

When making fibres of favourable mechanical properties, the solutionpreferably contains less than 0.8 wt. %, more particularly less than 0.5wt. %, of bound phosphorus.

Neutralisation may be carried out either immediately following thewashing step, or in between the coagulation and washing steps.Alternatively, neutralisation may take place after the washing step andbe followed by a next washing step. The neutralising agent used may beNaOH, KOH, LiOH, NaHCO₃, NH₄ OH, sodium ethanolate or sodiummethanolate, e.g., using a batchwise process, such as immersion, or acontinuous process, such as passing through a bath, spraying, the use ofa kiss roll, or a bath equipped with jet washers.

It was found that the susceptibility of the fibres to a heat treatmentcan be greatly reduced by the manner of aftertreatment of theextrudates. Such a process is disclosed in our co-pending patentapplication based on the Netherlands patent application NL 9401351.

The solution according to the present invention is especiallyadvantageous because its preparation and spinning can be carried out asa continuous process on a single line. In addition, the solution has theadvantage that when products are made therefrom, in particular when noconstituents other than phosphoric acid, water, and cellulose areemployed, the cellulose and the phosphoric acid react hardly, and hencethere is no, or hardly any, need for cellulose regeneration.

Thus are obtained in a highly advantageous manner cellulose fibresespecially suited to be used in rubber articles subjected to mechanicalload, such as vehicle tires, conveyor belts, rubber hose, and the like.The fibres are particularly suited to be used as a reinforcement invehicle tires, e.g., car and truck tires.

Fibres obtained by spinning the solution according to the invention werefound to have a good resistance to dynamic compression load. It wasfound that this resistance increases with the decreasing content ofphosphorus bound to cellulose in the solution. This resistance can bemeasured, e.g., by employing a so-called GBF (Goodrich Block Fatigue)test.

Generally speaking, the now found fibres constitute a favourablealternative to industrial yarns such as nylon, rayon, polyester, andaramid.

Further, the fibres can be pulped. Such pulp, which may be mixed withother materials, such as carbon pulp, glass pulp, aramid pulp,polyacrylonitrile pulp, or not, is highly suited to be used as areinforcing material, e.g., in asphalt, cement and/or frictionmaterials.

Properties of fibers obtained by spinning the anisotropic solution.

The invention also relates to the resulting cellulose fibres, which havevery good mechanical properties such as strength, modulus, andfavourable elongation. Since it is found that the solvent reacts withthe cellulose hardly, the properties obtained from the cellulosestructure, such as the chain modulus, are retained, while the anisotropyof the solution makes it possible to attain properties desired in manymechanical applications.

The properties of the fibres make them particularly suited for use intechnical applications.

Using the solution according to the present invention, fibres can beprepared having far better properties than the cellulose fibres known inthe art used in technical applications, e.g., Cordenka 660® and Cordenka700®, which are prepared using the so-called viscose process.

Using the solution according to the present invention cellulose yarnscan be made which have a breaking tenacity higher than 700 mN/tex, morein particular higher than 850 mN/tex, a maximum modulus at an elongationof less than 2% of at least 14 N/tex, and an elongation at break of atleast 4%, more in particular higher than 6%.

Due to the nature of the spinning solution and the coagulant, the fibrescontain from 0.02 to 1.3 wt. % of phosphorus bound to the cellulose ifthe fibres are coagulated in water or from 0.02 to 3.0 wt. % ofphosphorus bound to the cellulose if the fibres are coagulated in acoagulant which does not contain water and washed with water. Preferablythe fibres contain from 0.02 to 0.5 wt. % of phosphorus bound to thecellulose.

The filaments in a yarn bundle have a much higher compression strengththan filaments of prior art yarns, viz. from 0.30 to 0.35 GPa forfilaments obtained using the solution according to the present inventionin comparison with from 0.15 to 0.20 GPa for filaments of prior artyarns.

Furthermore, when the yarns are examined using Confocal Laser ScanningMicroscopy (CLSM), hardly any pores can be detected in the filaments,whereas filaments of prior art yarns show a large number of these pores.The same properties are found when small angle X-ray scattering is used.

In WO 85/05115 celluloseformate and regenerated cellulose multifilamentyarns spun from anisotropic phosphoric acid containing solutions arereported. The yarns show a morphology which appears to be built up oflayers embedded in each other, which surround the axis of the filaments,and which besides varies pseudoperiodically along the axis of thefilaments. In WO 94/17136 it is suggested that the morphology isconnected with the anisotropic solution from which the filaments areobtained.

Although the yarns according to the present invention are obtained froman anisotropic solution which contains phosphoric acid, the yarns do notshow a morphology as described in WO 85/05115.

Using wide angle X-ray diffraction, a crystal structure is found whichis similar to the crystal structure of prior art cellulose yarns. Thehalfwidths of some reflections in the diffration pattern can be used toestimate the size of crystalline regions in the yarn. It was found thatthe aspect ratio (crystal height/crystal width) of the yarns accordingto the invention is considerably higher than for prior art yarnsprepared using the viscose process, viz. from 4.3 to 5.0 and from 2.5 to3.5, respectively.

The sonic modulus of the yarns according to the invention reflects thehigher (tensile) modulus of these yarns. These higher moduli of theyarns according to the present invention probably reflects the highermolecular orientation of the cellulose molecules, which might be due tothe anisotropic nature of the spinning solution.

However, the higher modulus is not accompanied by a higher lateralbirefringence of the yarns, which is often found in fibres. For theyarns according to the invention a lateral birefringence smaller than11*10⁻⁴ is found, whereas for prior art yarns prepared using the viscoseprocess a lateral birefringence of from 12*10⁻⁴ to 26*10⁻⁴ is found.

Another measurement technique which clearly shows the difference betweenthe yarns according to the present invention and prior art yarns, isRaman Spectroscopy. This technique provides information about themolecular vibrations of a compound. Like other spectroscopic techniques,the spectrum recorded using this technique can be used as a kind offingerprint of the material. Major differences between the fibresaccording to the present invention and the prior art fibres are found inthe Raman spectrum between 100-600 cm⁻¹ and can be made morequantitatively by using hierarchical cluster analysis. Using thistechnique, the splitting between the yarns according to the presentinvention and prior art fibres, expressed as a heterogenuity value, islarger than 0.70.

It was found that only one of the above mentioned properties shows asignificant dependence on the amount of phosphorus bound to thecellulose, viz. the resistance to dynamic compression load, which can bemeasured using a fatigue test. Furthermore, it was found that therelative residual strength of the cellulose yarns after being tested islinear proportional to the amount of phosphorus bound to the cellulose.When the amount of phosphorus bound to the cellulose in a yarn isplotted (on the x-axis in wt. %) versus the relative residual strengthof a tested yarn (on the y-axis in % residual strength, i.e. % rs), aleast square linear regression computation of the data points reveals aregression coefficient, i.e. the slope of the linear fitted line throughthe data points, of from -30 to -70% rs/wt. %, more in particular offrom -40 to -60% rs/wt. %. It was found further that the constant termwhich results from the computation depends on the modulus of the testedyarn. A decrease of the modulus of the yarn is accompanied by anincrease of the constant term, thus at a constant amount of phosphorusbound to the cellulose, the relative residual strength of the fibresafter being tested is higher when the modulus of the fibres is lower.

In addition, the fibres possess good adhesion to rubber after a singleimpregnation with conventional adhesive, e.g., dipping with aresorcinol-formaldehyde latex (RFL) mixture.

Measurement techniques

Determination of birefringence Δn of the solution

The birefringence Δn was determined with the aid of an Abberefractometer type B, e.g., as described in W. H. de Jeu, Physicalproperties of Liquid Crystalline Materials (London: Gordon & Breach,1980), p. 35. The measurements were carried out at room temperature (20°C.), with use also being made of a Tamson oil bath to control thetemperature, a Eurotherm digital thermometer and type J thermo-couple, ahalogen lamp of 12V 20W. A polariser was used in the refractometer'socular lens. The index of refraction of the liquid was determined bymeasuring the angle of contact. The refractometer is constructed suchthat the index of refraction is given at the mavelength of the Na D-line(589.3 nm). This means that the dispersion of the index of refractionwas compensatred for. The birefringence an Δn=n∥-n_(l). In the isotropicphase Δn is 0 by definition.

Solutions are considered to be anisotropic if birefringence is observedin a condition of rest. Generally speaking, this holds for measurementscarried out at room temperature. However, within the framework of thepresent invention solutions which can be processed--e.g., by fibrespinning--at temperatures below room temperature and which displayanisotropy at said lower temperature are considered anisotropic also.Preference is given to solutions which are anisotropic at roomtemperature.

Visual determination of the isotropy or anisotropy was performed withthe aid of a polarisation microscope (Leitz Orthoplan-Pol (100×)). Tothis end about 100 mg of the solution to be defined were arrangedbetween two slides and placed on a Mettler FP 82 hot-stage plate, afterwhich the heating was switched on and the specimen heated at a rate ofabout 5° C./min. In the transition from anisotropic to isotropic, i.e.,from coloured to black, the temperature is read off at virtual black.The transition temperature is indicated as T_(ni) in °C.

The visual assessment during the phase transition was compared with anintensity measurement using a photosensitive cell mounted on themicroscope. For this intensity measurement a specimen of 10-30 μm wasarranged on a slide such that no colours were visible when crossedpolarisers were employed. Heating was carried out as described above.The photosensitive cell, connected to a recorder, was used to write theintensity as a function of time. Above a certain temperature (differingfor the different solutions) there was a linear decrease of theintensity. Extrapolation of this line to an intensity of 0 gave theT_(ni). In all cases, the value found proved a good match for the valuefound by the above-mentioned method.

Determination of DP

The degree of polymerisation (DP) of the cellulose was determined withthe aid of an Ubbelohde type 1 (k=0.01). To this end the cellulosespecimens to be measured were dried in vacuo for 16 hours at 50° C.after neutralisation, or the amount of water in the copper II ethylenediamine/water mixture was corrected to take into account the water inthe cellulose. In this way an 0.3 wt. % of cellulose-containing solutionwas made using a copper II ethylene diamine/water mixture (1/1). On theresulting solution the viscosity ratio (visc. rat. or ηrel) wasdetermined, and from this the limiting viscosity number (η) wasdetermined in accordance with the formula: ##EQU1## wherein c=celluloseconcentration of the solution (g/dl) and

k=constant=0.25

From this formula the degree of polymerisation DP was determined asfollows: ##EQU2##

Determining the DP of the cellulose in the solution proceeded asdescribed above after the following treatment:

20 g of the solution were charged to a Waring Blender (1 liter), 400 mlof water were added, and the whole was then mixed at the highest settingfor 10 minutes. The resulting mixture was transferred to a sieve andwashed thoroughly with water. Finally, there was neutralisation with a2%-NaHCO₃ solution for several minutes and after-washing with water. TheDP of the resulting product was determined as described above, startingfrom the preparation of the copper II ethylene diamine/water/cellulosesolution.

Determination of phosphorus content

The content of phosphorus bound to cellulose in the solution, or in acellulose product made from that solution, can be determined bycombining in a decomposition flask (a) 300 mg of cellulose solutionwhich has been coagulated, dried in vacuo for 16 hours at 50° C. afterthorough washing out using water, and then stored in a sealed samplevessel with (b) 5 ml of concentrated sulphuric acid and 0.5 ml of anYttrium solution containing 1000 mg/l of Yttrium. The cellulose iscarbonised with heating. After carbonisation, hydrogen peroxide is addedto the mixture in portions of 2 ml, until a clear solution is obtained.After cooling the solution is replenished with water to a volume of 50ml. With the aid of a phosphorus calibration line determined usingreference samples containing 100, 40, 20, and 0 mg/l of phosphorus,respectively, ICP-ES (Inductive Coupled Plasma-Emission Spectrometry) isused to determine the phosphorus content in the solution to be measuredby means of the following equation:

    phosphorus content (%)=(P.sub.conc (mg/l)50)/(C.sub.w (mg)*10)

wherein:

P_(conc) =the phosphorus concentration in the solution to be measuredand

C_(w) =the weighed out quantity of coagulated and washed cellulose.

Yttrium is added as an internal standard to correct the solutions'differing viscosities. The phosphorus content is measured at awavelength of 213.6 nm, the internal standard is measured at awavelength of 224.6 nm.

Determination of water content

The quantity of water absorbed by a fibre during coagulation in a waterbath or when the fibre is washed out with water can be determined bywashing the fibre with water and then removing the adhering moisturethrough filtering off with a buchner funnel. The moisture content (inwt. % vis-a-vis the dried fibre) can be determined by measuring thedecrease in weight as a result of heating for 20 minutes at 160° C.

Mechanical properties

The mechanical properties of the filaments and the yarns were determinedin accordance with ASTM standard 02256-90, using the following settings.

The filament properties were measured on filaments clamped with Arnitel®gripping surfaces of 10*10 mm. The filaments were conditioned for 16hours at 20° C. and 65% relative humidity. The length between grips was100 mm, the filaments were elongated at a constant elongation of 10mm/min.

The yarn properties were determined on yarns clamped with Instron 4Cclamps. The yarns were conditioned for 16 hours at 20° C. and 65%relative humidity. The length between clamps was 500 mm, the yarns wereelongated at a constant elongation of 50 mm/min. The yarns were twisted,the number of twists per meter being 4000/√linear density dtex!.

The linear density of the filaments, expressed in dtex, was calculatedon the basis of the functional resonant frequency (ASTM D 1577-66, Part25, 1968); the yarn's linear density was determined by weighing. Thebreaking tenacity, elongation, and initial modulus were derived from theload-elongation curve and the measured filament or yarn linear density.

The initial modulus (In. Mod.) was defined as the maximum modulus at anelongation of less than 2%.

Compression strength

The compression strength of filaments can be measured using theso-called Elastica test. In this test a filament loop is bent andstudied simultaneously under a microscope. In the elastic part of thecompressive stress-strain curve the shape of the loop remains unaltered.After a critical strain is reached the shape of the loop changessubstantially. The strain at which this change occurs is taken as thecritical compressive strain. As the compressive stress-strain curve isassumed to be the inverse of the tensile stress-strain curve, thecompressive strength is calculated from the filament (tensile)stress-strain curve as the stress at the strain which is equal to thecritical compressive strain. More information about the Elastica testcan be found, e.g., in D. Sinclair, J.Appl.Phys., 21, (1950), p.380-386.

Confocal Laser Scanning Microscopy (CLSM)

For inspection of a fibre sample using CLSM, light from an Ar/Kr laseris imaged through a pinhole, a beamsplitter, and objective lenses on thefibre sample. The reflected light is directed through the objectivelenses, the beamsplitter and a second pinhole to a photomultiplierdetector. Due to the optical configuration, only light coming from thefocal point of the objective lenses is imaged on the detector. Theadvantage of this kind of light microscopy is found, amongst others, ina high resolution (0.2 μm).

CLSM can be used in reflection and fluorescence mode. Reflection occursif a difference in refractive indices exists between adjacent parts of astructure. For cellulose fibres, with a rather low birefringence, thismeans that only defects can be made visible. The lower limit of the sizeof the defects which can be detected is approximately 100 nm.

In order to examine cellulose filaments using CLSM, 6-7 single filamentsare put on a glass plate, immersed in a liquid with a refrective indexof 1.48, and covered with thin glass plate. A 40× 1.3 N.A. oil immersionobjective lens was used to focus the laser beam on the sample.

X-ray diffraction

Wide-angle X-ray diffraction measurements on fibre samples wereperformed using a horizontal Philips X'pert MPD diffractometer.Cellulose fibre samples are wound on a metal frame and put in the sampleholder of the diffractometer. With this apparatus it is possible toadjust the scattering angle 2θ and the azimuthal angle φ independently.The X-ray beam was focussed using a parallel plate collimator. Theprogrammable divergence slit was fixed on 1/8°. Use was made of a copperfine focus X-ray tube.

Small-angle X-ray scattering photographs of the samples were made usinga Kiessig point focus camera. For the semi-quantitative evaluation ofthe equatorial scattering a Kratky line-focus camera with a linearposition sensitive counter was used.

A survey of the characterization of (cellulose) fibres with small-angleX-ray scattering can be found in Y. Cohen and E. L. Thomas,"Microfibrillar Network of a rigid rod polymer", Macromolecules, Vol.21, (1988), p. 436.

Lateral birefringence

The lateral birefringence of the cellulose fibres was measured using theDe Senarmonts method of compensation. To apply this method, a quarterwaveplate was positioned in parallel position in the compensator slot ofa De Senarmont compensator which was mounted in a Jenapol Interphako-Umicroscope equipped with Xenon illumination. Monochromatic light wasobtained by using a monochromator DISP-546 nm. Compensation is broughtabout by rotating the analyzer in the De Senarmont compensator. Theazimuth angle ω at compensation is read from the analyzer. The lateralbyrefringence is then calculated by dividing the optical path differencer (r=546*ω/180) by the thickness of the sample.

Samples can be prepared by embedding a fiber bundle in Spurr lowviscosity embedding material (Poly Sciences Inc.). The embedded sampleis then hardened for at least 16 hours at 70° C. Slices of about 2 mmthickness can be obtained by using a Struers Accutom equipped with anAbrasive Cut-off Wheel 5 PCS 357 CA. This is preferably done in such away that the fibers are cut through exactly perpendicular to their axis.The slices are then polished on both sides in subsequent steps withStruers Silicon carbide paper 1200 grit (14 μm), 2400 grit (10 μm), 4000grit (6 μm), DP-mol polishing cloth with Alumina Buhler Alpha 1 (5 μm),Alpha 1C (1 μm), and Struers Alumina AP F. In this way slices can beobtained with a thickness which is generally of from 10 to 40 μm. Thepolished slices are cemented onto a microscope glass with, e.g.,Locktide IS 401.

Raman spectroscopy

Raman spectra of cellulose fibres can be recorded with a Bruker RFS 100Fourier Transform Raman spectrometer equipped with a 1064 nm Nd:YAGlaser (Adlas, Model 421N). With this apparatus spectra can be recordedat a spectral resolution of 4 cm⁻¹ with a laser power of 1400 mW. Thediameter of the laser beam at the sample spot is approximately 30 μm.About 5000 scans are preferably collected for each spectrum. To performthe measurements, cellulose fibres are wrapped around a mirror andmounted in the sample stage of the spectrometer. Control measurementsshowed that cellulose fibres are not affected by the laser irradiation.

The IDENT-2 package from the OPUS software of Bruker can be used for thehierarchical cluster analysis of the spectra. In this analysis secondderivative spectra are used in the calculations. The analysis can beapplied to various spectral regions by using, e.g., Ward's algorithm.Details about the clustering procedure can be found in, e.g., D. Helm,H. Labischinski, G. Schallehn and D.Naumann, J.Gen.Microbiol, 137,(1991), 69 and D. Helm, H. Labischinski and D. Naumann,J.Microbiol.Methods, 14, (1991), 127.

Fatigue test

The resistance of a cellulose yarn to a dynamic compression load can bemeasured according to ASTM 0885-62T using a Goodrich Disk Fatiguetester. This test is often referred to as GBF fatigue test. For thistest a cellulose yarn is twisted into a two-fold cord at a helix angleof 25°. To promote the adhesion to rubber, the cord is impregnated witha resorcinol-formaldehyde latex. After impregnation, the cord isembedded in a Dunlop 5320 rubber and the rubber is vulcanised. Thesample is tested in the Fatigue tester for 6 hours, at 20% compressionand 0% elongation, and at 2375 cycles/minute. After being tested, thecord samples are prepared from the rubber, and the residual strength ismeasured. The relative residual strength is then calculated relative tothe strength of the impregnated cord before the fatigue test.

The invention will be further illustrated below with reference to theexamples.

Examples 1-3 relate to some properties of solutions comprisingcellulose, phosphoric acid, and water.

Examples 4 and 5 relate to the continuous preparation of anisotropicsolutions comprising cellulose, phosphoric acid, and water.

Examples 6-8 relate to the coagulation of fibres spun from anisotropicsolutions comprising cellulose, phosphoric acid, and water.

Examples 9-12 relate to the effect of the amount of phosphorus bound tocellulose on the appearance and the water content of fibres spun fromanisotropic solutions comprising cellulose, phosphoric acid, and water,which fibres are coagulated in water or acetone.

Examples 13-20 relate to spinning of fibres using anisotropic solutionscomprising cellulose, phosphoric acid, and water.

Unless otherwise specified, the following starting materials (listedtogether with their specifications) were used to prepare the solutionsin the examples.

    ______________________________________    mat.    manufacturer and code  P.sub.2 O.sub.5  %!    ______________________________________    P.sub.2 O.sub.5            J.T. Baker, 0193       98    H.sub.3 PO.sub.4            La Fonte Electrique SA, Bex Suisse,            crystallised, >99% (98,3% anal.)                                   71,2    H.sub.4 P.sub.2 O.sub.7            Fluka Chemika, 83210, 97% (98,8% anal.)                                   78,8    PPA*    Janssen Chimica, 84% min.                                   84    H.sub.2 O            demineralised          --    ______________________________________     *PPA = polyphosphoric acid

EXAMPLE 1

Solutions of cellulose, one or more phosphoric acids, and water wereprepared from compositions as indicated below.

The solutions were made by combining the phosphoric acids and mixingthem in an IKA-duplex type HKD 06 DP kneader (0.5 l) until a clear,viscous solution was obtained, cooling the liquid and adding thecellulose, and then continuing the kneading at room temperature (20° C.)for 25 minutes. The solution was assessed visually and the DP of thecellulose in the solution determined. For each composition the P₂ O₅content in the solvent (by definition the sum total of inorganicphosphoric acids, anhydrides, and water used) was calculated and listedin the table.

There is a certain connection between the properties listed under 2, 3,and 4. The more +indications a solution has, the stronger its anisotropyand the related favourable properties will be. Very good solutions have+indications only.

After preparation the solutions were assessed and characterised asfollows:

1+properly dissolved--undissolved;

2 +lustrous--opaque;

3 +anisotropic--isotropic;

4 +drawing threads--not drawing threads;

in measurements:

1 microscopic assessment, +if not more than 1/2% of the celluloseremains undissolved.

2 visual assessment during kneading.

3 via T_(ni) determination for dissolved portion's condition at 20° C.

4 visual assessment during kneading.

Solutions

Solutions containing 11.4 wt. % of cellulose were prepared by adding 12wt. % of cellulose (containing 5% of water) to the acid mixture aslisted in the table. The indicated P₂ O₅ content is the content in thesolvent, which, by definition, is made up of inorganic phosphoric acidsand water. The parts by weight of acid are the amounts of acid,calculated on the overall amount of acid employed, which were weighed into make the acid mixture to which the cellulose was added.

                  TABLE I    ______________________________________    parts by wt.                         Δn.                                              Tni  P.sub.2 O.sub.5    of acid.    DP     1     2   3   4   10.sup.4                                              ° C.                                                   %    ______________________________________    A    90,1   H.sub.3 PO.sub.4                        690  +   +   +   +   33   43   72         9,9    PPA    B    80,6   H.sub.3 PO.sub.4                        625  +   +   +   +   27   49   73         19,4   PPA    C    70,0   H.sub.3 PO.sub.4                        675  +   +   +   +   20   47   75         30,0   PPA    D    60,4   H.sub.3 PO.sub.4                        695  +   -   +   -   10   42   76         39,6   PPA    E    85,0   PPA          +   +   +   ±                                             10   39   71         15,0   H.sub.2 O    F    88,0   PPA     675  +   +   +   +   25   43   74         12,0   H.sub.2 O    G    90,1   PPA     685  +   +   +   +   40   46   75         9,9    H.sub.2 O    H    92,7   H.sub.4 P.sub.2 O.sub.7                        680  +   +   +   +   30   43   74         7,3    H.sub.2 O    I    74,8   P.sub.2 O.sub.5                        675  +   +   +   +   38   48   73         25,2   H.sub.2 O    J    80,0   PPA     695  +   -   -   ±     5    67         20,0   H.sub.2 O    K    69,7   H.sub.3 PO.sub.4                        588  ±                                 -   -   -             66         20,4   PPA         9,9    H.sub.2 O    L    80,0   H.sub.3 PO.sub.4                        670  ±                                 -   -   -             65         10,0   PPA         10,0   H.sub.2 O    M    79,9   H.sub.3 PO.sub.4                        685  -   -   -   -             57         20,1   H.sub.2 O    N    20,0   H.sub.3 PO.sub.4                        685  -   -   -   -             81         80,0   PPA    O    100,0  PPA          -   -   -   -             83    ______________________________________

It is clearly shown that when solutions containing 11.4 wt. % ofcellulose do not come within the limits of 65-80% of P₂ O₅ in thesolvent, the cellulose no longer dissolves. Just inside these limitsthere is what may be called a transition area. Dissolution at atemperature in excess of room temperature will give fairly good to goodsolutions for compositions such as listed under K and L. These solutionsare isotropic at room temperature. At a lower temperature they areanisotropic, and it is at this lower temperature that they can beprocessed into products to good effect.

EXAMPLE 2

In the same manner as described for Example 1 solutions containing 17.1wt. % of cellulose were made by adding 18 wt. % of cellulose (containing5% of water) to the acid compositions as mentioned in the table. Thepolyphosphoric acid (PPA) employed was ex Merck (85% P₂ O₅).

                  TABLE II    ______________________________________    parts by wt.                       Δn.                                            Tni  P.sub.2 O.sub.5    of acid.    1      2      3    4   10.sup.4                                            ° C.                                                 %    ______________________________________    A    100    H.sub.3 PO.sub.4                        ± ± +    ±                                           25        70    B    94,3   H.sub.3 PO.sub.4                        ± ± +    +   60   69   71         5,7    PPA    C    87,6   H.sub.3 PO.sub.4                        +    +    +    +   80   68   72         12,4   PPA    D    79,2   H.sub.3 PO.sub.4                        +    +    +    +   80   70   73         20,8   PPA    E*   60,5   H.sub.3 PO.sub.4                        +    +    +    +   75   71   76         39,5   PPA    F*   47,2   H.sub.3 PO.sub.4                        +    ± +    +   70   73   78         52,8   PPA    G*   42,2   H.sub.3 PO.sub.4                        +    -    +    ±                                           80   72   78         57,8   PPA    ______________________________________     *starting temperature selected for rapid dissolution procedure not lower     than 20° C.

EXAMPLE 3

A solvent was made of inorganic acids of phosphorus and water by heatingH₃ PO₄ to 43° C. and then cooling it and adding polyphosphoric acid suchthat the composition of the solvent for the various experiments wasapproximately the same at all times. The cellulose percentage wasvaried. For the preparation of the solutions use was made of the samestarting materials as listed in Example 2.

                  TABLE III    ______________________________________    parts by wt.                cell                          T.sub.ni                                                   P.sub.2 O.sub.5    of acid.     %!    DP     1   2   3   4   ° C.                                                   %    ______________________________________    A    80,3   H.sub.3 PO.sub.4                        7,6       +   +   ±                                              +   17*  73         19,7   PPA    B    80,6   H.sub.3 PO.sub.4                        11,4 625  +   +   +   +   49   73         19,4   PPA    C    79,2   H.sub.3 PO.sub.4                        17,1      +   +   +   +   70   73         20,8   PPA    D    77,5   H.sub.3 PO.sub.4                        24,7 560  +   +   +   +   82   73         22,5   PPA    E    79,0   H.sub.3 PO.sub.4                        28,5 400  +   +   +   +   93   73         21,0   PPA    F    81,0   H.sub.3 PO.sub.4                        38        ±                                      -   +   -   117  71         19,0   PPA    ______________________________________     *readily processable at 17° C.

EXAMPLE 4

In a Werner & Pfleiderer ZSK 30 twin-screw extruder a solution wasprepared continuously using cellulose and a solvent containing inorganicacids of phosphorus.

In the transport direction of the twin-screw extruder six pairs ofheating elements each of about 7.5 cm in length were arranged. Thesepairs of heating elements permit the setting of six differenttemperature zones in the transport direction of the extruder. In thefirst zone (zone 1) immediately beyond the throat of the twin-screwextruder a temperature of 0° C. was set. In the following zone (zone 2)a temperature of 10° C. was set. In the four subsequent zones (zones 3,4, 5, and 6) a temperature of 20° C. was set. Moreover, zone 4 and partsof zones 5 and 6 were kept under reduced pressure. The temperature ofthe heating element near the endplate of the extruder was set to 15° C.Powdered cellulose, Buckeye V65, DP 700, was added via the extruderthroat at a feeding rate of 2.2 kg/h. Via the first heating element inzone 1 a solution containing 80 wt. % of H₃ PO₄ (orthophosphoric acid)and 20 wt. % of PPA (polyphosphoric acid, ex Stokvis) was charged at afeeding rate of 7.8 kg/h.

At an extruder screw rate of rotation of 150 rpm an opticallyanisotropic cellulose solution containing less than 1 wt. % ofundissolved cellulose particles was formed in 10 minutes.

EXAMPLE 5

In a Conterna kneader with 6 chambers a solution was preparedcontinuously using cellulose and a solvent containing phosphoric acid.Cellulose (Buckeye V60 powdered cellulose, Dp=820) and the solvent, aliquid mixture of orthophosphoric acid and polyphosphoric acid (exStokvis) containing 74.4 wt. % P₂ O₅, were dosed in the inlet of thekneader at 3.0 kg/hr and 15.7 kg/hr, respectively. The temperature inthe chambers of the kneader was set to increase from 5° C. in chamber 1(with the inlet for the dosed components) to 15-20° C. in chamber 6(with an exit for the solution). The kneading and mixing elements inchambers 1-5 of the kneader were operated at a speed of 30-40 rpm, thekneading and mixing elements in chamber 6 were operated at a speed of3-8 rpm. In chambers 3-5 a reduced pressure of 40-60 mbar wasmaintained.

In this way an optically anisotropic solution was obtained containingless than 1 wt. % of undissolved particles. The residence time of thesolution in the kneader was estimated to be approximately 30 minutes.

EXAMPLE 8

A solvent was prepared by combining 80 parts by weight (pbw) of solidorthophosphoric acid (H₃ PO₄) and 20 pbw of polyphosphoric acid (exStokvis) in a Werner & Pfleiderer 2.51-Z kneader, type LUK 2.5 K3, andthen homogenising the mixture for at least 40 minutes at 48° C. After ahomogeneous liquid was obtained, it was cooled to 10° C., whereuponcellulose was added. Enough cellulose was added to give a final solutioncontaining 18 wt. % of cellulose (including equilibrium moisture). Inthis manner, with kneading of the mass, a homogeneous solution wasobtained in about 15 to 30 minutes and then degassed during the next 30minutes. The resulting solution was introduced into a storage vessel ona spinning machine, the temperature of the storage vessel and thespinning machine being 37° C. Next, the spinning solution was pressedthrough a spinneret with 100 capillaries each of a diameter of 65 μm.The samples were coagulated in water. The water content and thephosphorus content of the fibres were measured as a function of time(with t=0 being the moment at which the solution was heated to atemperature of 37° C.). The appearance of the fibres was also evaluated.The results are listed in Table IV.

                  TABLE IV    ______________________________________          Water    Phosph.    Time  content  content     min!  %!       %!      Appearance of the fibre    ______________________________________    25    425      0.45     somewhat swollen fibres, individual                            fibres still visible    60    375      0.60     somewhat swollen fibres, individual                            fibres still visible    110   425      0.90     somewhat swollen fibres, individual                            fibres still visible    150   490      1.35     somewhat swollen fibres, individual                            fibres still visible    180   570      1.50     swollen fibres, no individual                            fibres visible    240   615      1.90     swollen fibres, no individual                            fibres visible    300   640      2.15     swollen fibres, no individual                            fibres visible    ______________________________________

EXAMPLE 7

In the same manner as described in Example 6 a cellulose-containingsolution was prepared. The solvent was made by intermixing 66.1 pbw oforthophosphoric acid and 33.9 pbw of polyphosphoric acid (ex Stokvis).

In the same manner as described in Example 6 the solution was pressedthrough a spinneret. One portion of the samples was coagulated in water,another was coagulated in acetone. For both types of coagulated samplesthe water and phosphorus contents were determined as a function of time.The appearance of the fibres was also evaluated. The results for thewater coagulated samples are listed in Table V, those for the acetonecoagulated samples are listed in Table VI.

                  TABLE V    ______________________________________    Water coagulation          Water    Phosph.    Time  content  content     min!  %!       %!      Appearance of the fibre    ______________________________________    30    460      1.04     somewhat swollen fibres, individual                            fibres still visible    50    560      1.49     swollen fibres, no individual                            fibres visible    90    780      2.50     very strongly swollen thread    125   1160     2.91     very strongly swollen thread    155   3230     3.55     gel formation    ______________________________________

                  TABLE VI    ______________________________________    Acetone coagulation          Water    Phosph.    Time  content  content     min!  %!       %!      Appearance of the fibre    ______________________________________    75    400      2.01     somewhat swollen fibres, individual                            fibres still visible    120   490      2.90     somewhat swollen fibres, individual                            fibres still visible    150   960      3.49     very strongly swollen thread    190   3460     4.28     gel formation    ______________________________________

EXAMPLE 8

In the same way as described in Example 6 a cellulose-containingsolution was prepared. The solvent was made by intermixing 57.9 pbw oforthophosphoric acid and 42.1 pbw of polyphosphoric acid.

In the same way as described in Example 6 the solution was pressedthrough a spinneret plate. One portion of the samples was coagulated inwater, another coagulated in acetone. For both types of coagulatedsamples the water and phosphorus contents were determined as a functionof time. The appearance of the fibres was also evaluated. The resultsfor the water coagulated samples are listed in Table VII, those for theacetone coagulated samples are listed in Table VIII.

                  TABLE VII    ______________________________________    Water coagulation            Water   Phosph.    Time    content content     min!    %!      %!       Appearance of the fibre    ______________________________________    15      620     1.71      swollen fibres, no individual                              fibres visible    35      670     2.32      swollen fibres, no individual                              fibres visible    50      910     2.94      very strongly swollen thread    70      1790    3.46      gel formation    95      7650    5.90      gel formation    ______________________________________

                  TABLE VIII    ______________________________________    Acetone coagulation          Water    Phosph.    Time  content  content     min!  %!       %!      Appearance of the fibre    ______________________________________    25    430      2.04     somewhat swollen fibres, individual                            fibres still visible    45    460      2.69     somewhat swollen fibres, individual                            fibres still visible    75    1600     3.67     gel formation    135   8250     5.62     gel formation    ______________________________________

EXAMPLE 9

A solvent was prepared by mixing and kneading 69.1 pbw oforthophosphoric acid (71.2% P₂ O₅) and 13.5 pbw of polyphosphoric acid(84.5% P₂ O₅) at 60° C. in vessel until a clear, viscous liquid wasobtained. The liquid was transferred to a Linden-Z kneader, heated to35° C. and further homogenised. After 110 minutes of homogenisation theliquid was cooled down to 4° C. In this way a solvent was preparedcomprising 74.3 wt. % P₂ O₅. At this temperature 0.88 pbw water and 16.0pbw cellulose powder (Buckeye V65) containing 5.6 wt. % of water wereadded. The components were thoroughly kneaded for 18 minutes, the last13 of them under vacuum, until a homogeneous solution was obtained. Thesolution was thus prepared using a solvent composed of 72.7 wt. % P₂ O₅.

Using a spinning pump this solution was passed to a spinneret via aconveying pipe having a temperature of approximately 25° C. The solutionwas spun out at approximately 36° C. through a spinneret with 375capillaries each of a diameter of 65 μm, via an air gap of 30 mm, to acoagulation bath filled with different coagulants at 20° C. After beingpassed through this bath (about 0.5 meter) the resulting filament yarnswere washed with water at 15° C. using jet washers and neutralised usinga 2.5 wt. % Na₂ CO₃ ·10H₂ O solution. After neutralisation the yarnswere washed again with water using jet washers, dried on a drying godetat 150° C. and wound onto a bobbin at a speed of 30 m/min.

Cellulose yarns were manufactured as indicated above using methanol,ethanol, and acetone as coagulants. The mechanical properties of thefibres so obtained are listed in TABLE IX.

                  TABLE IX    ______________________________________              breaking     elongation                                    initial              tenacity     at break modulus    Coagulant  mN/tex!      %!       N/tex!    ______________________________________    methanol  430          5,1      17,2    ethanol   450          4,7      17,4    acetone   630          5,4      19,4    ______________________________________

EXAMPLE 10

Cellulose yarns were manufactured as indicated in example 9 usingn-propanol, n-butanol, n-pentanol, and acetone as coagulants. Themechanical properties of the fibres so obtained are listed in TABLE X.

                  TABLE X    ______________________________________              breaking     elongation                                    initial              tenacity     at break modulus    Coagulant  mN/tex!      %!       N/tex!    ______________________________________    n-propanol              730          5,3      22,0    n-butanol 600          5,0      21,0    n-pentanol              341          4,4      15,7    acetone   610          5,2      20,2    ______________________________________

EXAMPLE 11

Cellulose yarns were manufactured as indicated in example 9 usingbutanone, 2-pentanone, cyclopentanone, cyclohexanone, and acetone ascoagulants. The mechanical properties of the fibres so obtained arelisted in TABLE XI.

                  TABLE XI    ______________________________________               breaking    elongation                                    initial               tenacity    at break modulus    Coagulant   mN/tex!     %!       N/tex!    ______________________________________    butanone   730         6,6      19,8    2-pentanone               650         5,9      19,5    cyclopentanone               480         4,3      19,0    cyclohexanone               600         5,3      19,0    acetone    780         6,0      21,1    ______________________________________

EXAMPLE 12

Cellulose yarns were manufactured as indicated in example 9 usingmethylformate, methylacetate, ethylacetate, and acetone as coagulants.The mechanical properties of the fibres so obtained are listed in TABLEXII.

                  TABLE XII    ______________________________________               breaking    elongation                                    initial               tenacity    at break modulus    Coagulant   mN/tex!     %!       N/tex!    ______________________________________    methylformate               650         5,5      19,6    methylacetate               650         5,5      19,1    ethylacetate               690         6,5      18,8    acetone    640         5,5      19,3    ______________________________________

EXAMPLE 13

A solution was prepared from 62.8 parts by weight (pbw) oforthophosphoric acid (98.3%), 17.4 pbw of polyphosphoric acid (84% P₂O₅), 18.8 pbw of powdered cellulose (DP 700), and 1 pbw of water derivedfrom the cellulose, in the following manner: the acids were mixed in anIKA-duplex type HKD-T 06D kneader (0.5 l) and heated until a clear,viscous solution was obtained. Next, powdered cellulose was added andover 25 minutes the kneader was cooled down to room temperature, 10minutes thereof with degassing. The P₂ O₅ content in the solvent wascalculated to be 73%.

The obtained solution was fed via a filter (2*120 mesh, 25 μm) to aspinning machine provided with a spinneret with 30 orifices of 70 μmeach. At a jet velocity of 3 m/min and a temperature of 25° C.extrudates were formed, which after passing through an air gap of 25 mmwere guided to an acetone bath of -20° C. of about 1 meter in length.After being passed through this bath the obtained filaments were woundonto a spool and then washed with water for about 30 minutes at atemperature of 25° C. Measurements were carried out on the resultingfilaments in accordance with the aforementioned procedures. Themeasurements were performed on several filaments.

                  TABLE XIII    ______________________________________    linear   breaking      elon-   initial    density  tenacity      gation  modulus     dtex!    mN/tex!       %!      N/tex!    ______________________________________    3,2      520           5,4     21    3,1      750           6,8     23    2,5      560           5,6     21    2,1      580           4,6     25    ______________________________________

EXAMPLE 14

A solution was prepared from 67.6 pbw of orthophosphoric acid (98.3%),16.5 pbw of polyphosphoric acid (84.5% P₂ O₅), 15.1 pbw of powderedcellulose (DP 700), and 0.8 pbw of water. The preparation of thesolution was as follows:

Orthophosphoric acid was introduced into a Linden-Z kneader with anextruder discharge and melted down. Next, the polyphosphoric acid wasadded. After a clear, viscous solution had been obtained, there wascooling to 25° C. and immediately afterwards the powdered cellulose wasadded. The liquid was cooled with kneading. The maximum temperature ofthe obtained liquid was 37° C. for about 5 minutes. Kneading wascontinued for 30 minutes, the last 15 of them with degassing. The P₂ O₅content in the solvent was calculated to be 73.0%.

The resulting solution was fed to a spinning machine having a 5 μmfilter and a spinneret with 250 orifices of 65 μm each. At a jetvelocity as indicated below and a temperature of 46° C. extrudates wereformed, which after being passed through an air gap of 25 mm were guidedto an acetone bath of -12° C. After being passed through this bath (ofabout 0.6 meter) the obtained filaments were washed in a 4 m long waterbath (T=35° C.) equipped with jet washers. The winding speed was 100m/min at all times, the degree of drying and the moisture content of theyarn are indicated below.

The DP of the cellulose was determined at the outset and was 700, the DPfor the solutions and the yarns is listed below.

The properties of the obtained yarns were determined in accordance withprocedures mentioned hereinbefore.

Cellulose yarns were manufactured as indicated above, the jet velocitybeing 22.3 m/min. After washing the resulting yarn was finished anddried on an electrically heated roller at 70° C. until it had a moisturecontent of about 40%.

The measurements were performed on the obtained fibre bundles after theyhad been twisted at 214 twists per meter. The DP of the cellulose in thesolution was 545, the DP of the obtained fibres 510. The phosphoruscontent in the yarn was determined and found to be 1%. The properties ofthe yarns are listed in TABLE XIV.

                  TABLE XIV    ______________________________________             linear  breaking   elongation                                       initial    ex.      density tenacity   at break                                       modulus    no.       dtex!   mN/tex!    %!     N/tex!    ______________________________________    1        351     620        5,3    18,2    2        351     620        5,4    17,8    3        351     560        4,7    18,2    4        351     550        4,7    17,9    5        351     500        4,6    18,0    average          570        4,9    18,0    ______________________________________

EXAMPLE 15

Into a Linden-Z kneader with extruder discharge were charged 16,240 g ofa solution containing 74.3 wt. % of P₂ O₅ and 25.6 wt. % of water. Thissolution was obtained by mixing orthophosphoric acid and polyphosphoricacid in the proper ratio. This clear solution was kneaded for some timeat 30°-50° C. After cooling water was added to the solution. After theaddition of the water the solution contained 73.1 wt. % of P₂ O₅ and26.9 wt. % of water, and the temperature of the solution was 6° C.Immediately after the addition of the water 3,600 g of powderedcellulose were added. After the feeding of the cellulose the solutioncontained 18 wt. % of cellulose (including the equilibrium moisture ofthe cellulose). The mixture was kneaded for 30 minutes until ahomogeneous solution was obtained. Using a spinning pump this solutionwas passed to a spinneret via a conveying pipe having a temperature of30° C. The solution was spun out at 60° C. through the spinneret with375 capillaries each of a diameter of 65 μm, via an air gap of 30 mm, toa coagulation bath filled with acetone at a temperature of +12° C. Thedraw ratio in the air gap was about 7. Next, the yarn was washed withwater having a temperature of 44° C. and neutralised with 2.5 wt % Na₂CO₃ ·10H₂ O solution in water. After neutralisation the yarn was driedand wound at a rate of 120 m/min.

In this way a yarn spun 200 minutes after the addition of the powderedcellulose was obtained, which had a phosphorus content of 0.47%. Theyarn had a breaking tenacity of 800 mN/tex, an elongation at break of5.8%, and a maximum modulus at an elongation of less than 2% of 22.4N/tex.

EXAMPLE 16

Into a Linden-Z kneader with extruder discharge were charged 14,130 g ofa solution containing 74.3 wt. % of P₂ O₅ and 25.6 wt. % of water. Thissolution was obtained by mixing orthophosphoric acid and polyphosphoricacid in the proper ratio. This clear solution was kneaded for some timeat 30°-50° C. After cooling water was added to the solution. After theaddition of the water the solution contained 73.1 wt. % of P₂ O₅ and26.9 wt. % of water, and the temperature of the solution was 7° C.Immediately after the addition of the water 2,700 g of powderedcellulose were added. After the feeding of the cellulose the solutioncontained 16 wt. % of cellulose (including the equilibrium moisture ofthe cellulose). The mixture was kneaded for 35 minutes until ahomogeneous solution was obtained. Using a spinning pump this solutionwas passed to a spinneret via a conveying pipe having a temperature of25° C. The solution was spun out at 60° C. through the spinneret with375 capillaries each of a diameter of 65 μm, via an air gap of 40 mm, toa coagulation bath filled with acetone at a temperature of +11° C. Thedraw ratio in the air gap was about 6. Next, the yarn was washed withwater having a temperature of 44° C. and neutralised with 2.5 wt % Na₂CO₃ ·10H₂ O solution in water. After neutralisation the yarn was driedand wound at a rate of 120 m/min.

In this way a yarn spun 120 minutes after the addition of the powderedcellulose was obtained, which had a phosphorus content of 0.25%. Theyarn had a breaking tenacity of 860 mN/tex, an elongation at break of6.7%, and a maximum modulus at an elongation of less than 2% of 22.1N/tex.

EXAMPLE 17

In a Werner & Pfleiderer ZSK 30 twin-screw extruder as described inExample 4, an anisotropic solution comprising cellulose, phosphoricacid, and water was prepared continuously and was directly spun into amultifilament yarn.

Powdered cellulose Buckeye V60, DP=820 was dosed in the throat of theextruder at a feeding rate of 0.8 kg/hr. Directly after the troat of theextruder a liquid mixture comprising 74.4 wt. % of P₂ O₅ and water wasdosed at a feeding rate of 4.2 kg/hr. The extruder screws were operatedat 250 rpm. The temperature in zone 1 of the extruder was set to 0° C.,the temperature in zone 2 was set to 10° C., and the temperature inzones 3-7 was set to 20° C. The temperature of the outlet of theextruder was set to 10-15° C. In zones 4, 5, and 6 a reduced pressure of40-60 mbar was maintained.

The obtained anisotropic solution contained less than 1 wt. % ofundissolved particles. Using several spinning pumps this solution waspassed through several filters to a spinneret via a conveying pipe. Thissolution was heated to 52° C. and spun through the spinneret at 59° C.with 375 capillaries each of a diameter of 65 μm, via an air gap of 42mm, to a coagulation bath filled with acetone at temperature of 10° C.Next, the yarn was washed with water at a temperature of 20° C. andneutralised. After neutralisation with a 2.5 wt. % Na₂ CO₃ ·10H₂ Osolution in water, the yarn was washed again with water at a temperatureof 15° C., dried at 150° C. to a water content of 8.5 wt. %, and woundat a rate of 120 m/min.

The obtained yarns had a DP of approximately 610, a content ofphosphorus bound to cellulose of approximately 0.50%, a yarn count of625-635 dtex, a breaking tenacity of 760-775 mN/tex, an elongation atbreak of 6.3-6.7% and a maximum modulus at an elongation of less than 2%of 19-21 N/tex.

EXAMPLE 18

In a Werner & Pfleiderer ZSK 30 twin-screw extruder as described inExample 4, an anisotropic solution comprising cellulose, phosphoricacid, and water was prepared continuously and was directly spun into amultifilament yarn.

Powdered cellulose Buckeye V65, DP=700 was dosed in the throat of theextruder at a feeding rate of 1.5 kg/hr. Directly after the troat of theextruder a liquid mixture comprising 74.4 wt. % of P₂ O₅ and water wasdosed at a feeding rate of 8.8 kg/hr. The extruder screws were operatedat 300 rpm. The temperature in zone 1 of the extruder was set to 0° C.,the temperature in zone 2 was set to 10° C., and the temperature inzones 3-7 was set to 20° C. The temperature of the outlet of theextruder was set to 10-15° C. In zones 4, 5, and 6 a reduced pressure of40-60 mbar was maintained.

The obtained anisotropic solution contained less than 1 wt. % ofundissolved particles. Using several spinning pumps this solution waspassed through several filters to a cluster spinning assembly via aconveying pipe. This solution was heated to 60° C. and spun through thespinning assembly with 4×375 capillaries each of a diameter of 75 μm at57° C., via an air gap of 30 mm, to a coagulation bath filled withacetone at temperature of 12° C. Next, the yarn was washed with water ata temperature of 20° C. and wound at a rate of 100 m/min. In a separatestep the yarn was neutralised with a 2.5 wt. % Na₂ CO₃ ·10H₂ O solutionin water, washed again with water at a temperature of 15° C., dried, andwound at a rate of 30 m/min.

The obtained yarn had a DP of 590, a content of phosphorus bound tocellulose of 0.22%, a yarn count of 2345 dtex, a breaking tenacity of620 mN/tex, an elongation at break of 5.7% and a maximum modulus at anelongation of less than 2% of 19.1 N/tex.

EXAMPLE 19

In a Werner & Pfleiderer ZSK 30 twin-screw extruder as described inExample 4, an anisotropic solution comprising cellulose, phosphoricacid, and water was prepared continuously and was directly spun into amultifilament yarn.

Powdered cellulose Buckeye V60, DP=820 was dosed in the throat of theextruder at a feeding rate of 1.5 kg/hr. Directly after the troat of theextruder a liquid mixture comprising 74.4 wt. % of P₂ O₅ and water wasdosed at a feeding rate of 8.87 kg/hr. The extruder screws were operatedat 300 rpm. The temperature in zone 1 of the extruder was set to 0° C.,the temperature in zone 2 was set to 10° C., and the temperature inzones 3-7 was set to 20° C. The temperature of the outlet of theextruder was set to 10-15° C. In zones 4, 5, and 6 a reduced pressure of40-60 mbar was maintained.

The obtained anisotropic solution contained less than 1 wt. % ofundissolved particles. Using several spinning pumps this solution waspassed through several filters to a cluster spinning assembly via aconveying pipe. This solution was heated to 55° C. and spun through thespinning assembly with 4×375 capillaries each of a diameter of 65 μm at58° C., via an air gap of 25 mm, to a coagulation bath filled withacetone at temperature of 10° C. Next, the yarn was washed with water ata temperature of 20° C. and neutralised with a 2.5 wt. % Na₂ CO₃ ·H₂ Osolution in water. After neutralisation the yarn was washed again withwater at a temperature of 30° C. using jet washers, dried at 150° C.,and wound at a rate of 100 m/min.

The obtained yarns had a yarn count of 2550 dtex, a breaking tenacity of720-730 mN/tex, an elongation at break of 6.5-6.9% and a maximum modulusat an elongation of less than 2% of 15.5-17.5 N/tex.

We claim:
 1. A process for making cellulose extrudates from an opticallyanisotropic solution, 94-100% of which comprises the followingconstituents:cellulose, phosphoric acid and/or its anhydrides, andwater; and 0-6 wt % of other constituents, wherein the solution is spunby an air gap spinning process, with the extrudates obtained by thisprocess being coagulated in a coagulant.
 2. The process of claim 1,wherein the coagulant has a temperature of less than 30° C.
 3. Theprocess of claim 1, wherein the coagulant is an alcohol, ketone, ester,or water, or a mixture of two or more of these constituents.
 4. Theprocess of claim 1, wherein the coagulant is isopropanol, n-propanol,acetone, or butanone, or a mixture of these constituents with water. 5.The process of claim 1, wherein the extrudates after being coagulatedare washed with water.
 6. The process of claim 1, wherein the extrudatesare fibers.
 7. A cellulose fiber having the following properties:abreaking tenacity higher than 700 mN/tex, a maximum modulus at anelongation of less than 2% of at least 14 N/tex, an elongation at breakof at least 4%, and a content of phosphorus bound to cellulose of from0.02 to 1.3 wt. %.
 8. The cellulose fiber of claim 7, wherein thecontent of phosphorus bound to cellulose is from 0.02 to 0.5 wt. %. 9.The cellulose fiber of claim 7 having a compression strength of from0.30 to 0.35 GPa.
 10. A rubber article which can be subjected tomechanical load containing a reinforcing yarn of cellulose, wherein thereinforcing yarn comprises fibers of claim
 7. 11. A vehicle tirecontaining reinforcing yarn of cellulose wherein the reinforcing yarncomprises fibers of claim
 7. 12. The cellulose fiber of claim 7, whereinthe breaking tenacity is higher than 850 mN/tex.
 13. The cellulose fiberof claim 7, wherein the elongation at break is higher than 6%.
 14. Thecellulose fiber of claim 8, having a compression strength of from 0.30to 0.35 GPa.
 15. The cellulose fiber of claim 7, wherein the lateralbirefringence is smaller than 11×10⁻⁴.